A search engine is an information retrieval system designed to help find information from one or more sources. A web search engine typically retrieves information from an open data source such as the World Wide Web but search engines can be targeted at any number of data sources, including other search engines. Search engines that search multiple sources and aggregate the results are often called “federated search engines” and sometimes “meta search engines”. When a federated search engine queries another search engine, often the only way to retrieve the results is via the same result page the target search engine displays to users. The federated search engine must then extract each result and its fields from the result page before the results can be aggregated. Effectively extracting this data is a common problem for federated search engines. There are different tools for dissociating the information of interest from the entire data that is retrieved. One technique for accomplishing such dissociation is by means of regular expressions. Regular expressions consist of meta-text written in a formal language that other programs can use to match text patterns and extract values occurring within the match. Regular expressions are the key to powerful flexible and efficient text processing.